1. Field of the Invention
The present invention relates generally to integrated circuits, and more particularly to integrated, impedance matching, termination circuits.
2. Background
Advances in semiconductor manufacturing technologies have allowed circuit designers to integrate tremendous numbers of transistors on a single die. For example, modern integrated circuits (ICs) commonly include several million transistors interconnected on a single, small substrate. Typically, these are field effect transistors (FET). At the same time, computer architecture, and more particularly processor architecture, has gone in the direction of emphasizing shorter and shorter cycle times. These advances in semiconductor manufacturing and processor architecture have led to the production of very high-speed integrated circuits.
Many electronic systems, including but not limited to computer systems, are made up of a number of integrated circuits, each of which operates at high speed. The various integrated circuits are typically electrically interconnected by means of one or more buses. These buses are typically collections of physical interconnection signal lines that provide communication pathways between and among the various integrated circuits. As is known in this field, the signals that are transferred over the buses between the integrated circuits may represent such things as data, instructions, or control information. In order to obtain the most benefit from the high-speed operational capabilities of these integrated circuits, it is generally desirable to communicate over the buses at a high data transfer rate.
Various techniques have been developed for facilitating high-speed electrical communication over buses. For example, reducing the voltage swing that is required to distinguish between a logical one and a logical zero, also reduces the amount of time that is required for a signal transition and therefore provides for faster operation. Another technique that is useful for enabling high-speed communication over buses is the use of termination devices. Proper termination of signal lines reduces or eliminates the problems caused by signal reflections. Typically, a termination device is implemented as a resistor that is coupled between a signal line and a power supply node.
What is needed are circuits and methods for providing low-cost, area-efficient, impedance-matched termination for transmission lines.